Citation 5 tubes

[DennisK2021]

Posting here instead of the owner's thread for more responses. I have parts coming for my Citation 5 but it did not come with power tubes. It looks like the 7581A may be preferred. I'm only seeing Tung Sol as a current manufacturer.

Per Wiki, (may be dated) "Some modern Russian manufacture Sovtek KT66 tubes are actually 6L6GC tubes in a KT66 style bottle. While these tubes have the same pinout and minimum tolerances required of a KT66 tube, they do not have the performance characteristics of a true kinkless tetrode KT66 tube.

"By contrast the very latest Russian manufactured tubes (2012) not only carry the same internal electrode structure as the original KT66 (they now look the same) they also have the same rugged electrical characteristics and can withstand a high voltage on grid 2 comparable to the anode voltage rating, allowing greater power output afforded by higher voltage capability when run in ultralinear connection."

That, to me, means seeking vintage tubes might not be a good idea, but anybody know of good vintage tubes or should I just get the Tung Sol?

Edit: Now it looks like the Tung Sol are discontinued. The options seem to be Shuguang (Chinese), Genalex Gold Lion (Russian) or JJ (Slovakia).

Also curious what tubes were originally used in the Cit 5.

 

[maxhifi]

The "real" KT66 is a British tube. The 7581A is an American tube that is often dual branded 7581A/KT66, but is really more similar to a 6L6GC than the British KT66.

What I'm saying is, for your citation, just get some good 6L6GC tubes, and don't worry about getting KT66s for it.

 

[gadget73]

Does the CitV actually need the 7581A ? Those have an extra 5 watts plate dissipation over the 7581 or 6L6GC which is pretty nearly the same, and a lot more options in new and old production.

 

[Hi-FiGuy]

The Citaton V may not have enough filament current to run KT66 tubes, they require more than 7581 or 6L6GC. Its best to just run 6L6GC tubes and watch for red plating. If they are running a bit hot check that the bias voltage is correct or slightly higher than normal.

 

[Mr Boochie]

If you can find a US-made GE or Philips ECG 7581A. Those make the "biggest" sound of the 6L6GC variants. They are rated for a maximum dissipation of 35 watts.

 

[DennisK2021]

Does the CitV actually need the 7581A ? Those have an extra 5 watts plate dissipation over the 7581 or 6L6GC which is pretty nearly the same, and a lot more options in new and old production.

The Citaton V may not have enough filament current to run KT66 tubes, they require more than 7581 or 6L6GC. Its best to just run 6L6GC tubes and watch for red plating. If they are running a bit hot check that the bias voltage is correct or slightly higher than normal.

I thought that a higher-spec tube downgraded into an under-volted circuit is fine; the inverse cooks the tube. Are you guys saying the tube will draw more power because the plate dissipation is higher?

I haven't looked at the KT data sheet. The on-line stores no longer have 7581 Tung Sol, those have been replaced by 7581A. The 6L6GCs are 5881s in my searches. The Cit came with nice SovTek 5881s but the evaluating engineer suggested putting the correct tubes in.

If you can find a US-made GE or Philips ECG 7581A. Those make the "biggest" sound of the 6L6GC variants. They are rated for a maximum dissipation of 35 watts.



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From eBay 6 GE 7581A. Twice the price of 4 new, matched tubes for 80% vintage tubes. I will think about it. I'm missing Jesse but suspect I wouldn't pay for NOS at the moment. Not sure how long it will take to get the Cit working but I'll want something reliable and affordable to start. Maybe the 5881s it came with?

My goal is to power a pair of AR3a speakers with this amp.

 

[maxhifi]

I thought that a higher-spec tube downgraded into an under-volted circuit is fine; the inverse cooks the tube. Are you guys saying the tube will draw more power because the plate dissipation is higher?

The 7581A is not a KT66, they are different tubes. The KT66 pulls more filament current than a 6L6GC, 7581A, or any other American 6L6 tube, where all American 6L6 tubes need 0,9A. "higher rated" means they can take more voltage, or power, but the filament current is a separate thing to consider.

I haven't looked at the KT data sheet. The on-line stores no longer have 7581 Tung Sol, those have been replaced by 7581A. The 6L6GCs are 5881s in my searches. The Cit came with nice SovTek 5881s but the evaluating engineer suggested putting the correct tubes in.

Sovtek coin base 5881s are excellent tubes, and the maximum ratings are fine but are not an exact match to the American 6L6 in terms of characteristics. I would probably not want to use them either in this application, would prefer any modern 6L6GC. The original US made 5881 is a totally different tube than the Sovtek, I would not use an American 5881 in your amplifier, the ratings are just way too low. Sovtek applied 5881 to the Russian 6P3EV in the 1990s, because nobody in the US would have any idea what is a 6P3EV and has managed to confuse everyone for the last 35 years.

View attachment 3848671

From eBay 6 GE 7581A. Twice the price of 4 new, matched tubes for 80% vintage tubes. I will think about it. I'm missing Jesse but suspect I wouldn't pay for NOS at the moment. Not sure how long it will take to get the Cit working but I'll want something reliable and affordable to start. Maybe the 5881s it came with?

My goal is to power a pair of AR3a speakers with this amp.

The 6L6GC is a fine substitute, Keep in mind your amplifier asks for the 7581, not the 7581A, so the lower ratings of the 7581 are perfectly fine, and they happen to match the 6L6GC exactly. There's more selection of new 6L6GC than 7581, since Fender guitar amplifiers use them, and you may even find some sitting on the shelf at a local guitar store for reasonable money.

 

[gadget73]

The KT66 pulls more filament current than a 6L6GC, 7581A, or any other American 6L6 tube, where all American 6L6 tubes need 0,9A. "higher rated" means they can take more voltage, or power, but the filament current is a separate thing to consider.

exactly, you can use a tube rated for 35 watts plate dissipation in a circuit that only needs 30 but only if it can be lit. I have no idea what the CitV power transformer is rated for but broadly speaking its not a great idea to draw significantly more than it was designed for just in case there isn't much extra headroom

The 6L6GCs are 5881s in my searches.

6L6GC is rated for 30 watts, 5881 is less, offhand I want to say 23 but there may be design center vs design max rating differences and bad memory involved here.
.

Sovtek applied 5881 to the Russian 6P3EV 1990s, because nobody in the US would have any idea what is a 6P3EV and has managed to confuse everyone for the last 35 years.

have heard endless argument about whether these are or are not a 30w class 6L6GC equivalent. I don't know, though I do own a set. They sound good in an amp I built around them but I don't have any old production 6L6GC to do any sort of real comparison. I've heard they are more of a 5881, have also heard that they have higher Rp so its not really that either.

 

[maxhifi]

exactly, you can use a tube rated for 35 watts plate dissipation in a circuit that only needs 30 but only if it can be lit. I have no idea what the CitV power transformer is rated for but broadly speaking its not a great idea to draw significantly more than it was designed for just in case there isn't much extra headroom

6L6GC is rated for 30 watts, 5881 is less, offhand I want to say 23 but there may be design center vs design max rating differences and bad memory involved here.
.

Cit V manual calls for 7581, which has 30W max plate rating just like 6L6GC... no need to even check anything. The 7581A at 35W is more robust than the 6L6GC or 7581, but it's not relevant, because the amplifier does not require a 7581A.

 

[Mr Boochie]

Cit V manual calls for 7581, which has 30W max plate rating just like 6L6GC... no need to even check anything. The 7581A at 35W is more robust than the 6L6GC or 7581, but it's not relevant, because the amplifier does not require a 7581A.

You know what is ironic? I've had Harmon-Kardon labeled V-pulls of GE-made (Owensboro, KY) tan-based 7581A tubes.

They are great tubes. And sound great — even biased to the 6L6GC output (30 watts vs. 35 watts max).

Beautiful tubes. They don't make them like this anymore.

 

[maxhifi]

You know what is ironic? I've seen Harmon-Kardon labeled V-pulls of GE-made (Owensboro, KY) tan-based 7581A tubes.

They are great tubes. And sound great — even biased to the 6L6GC output (30 watts vs. 35 watts max).

Beautiful tubes. They don't make them like this anymore.

You've got an amazing tube collection!

 

[Mr Boochie]

You've got an amazing tube collection!

Thanks. The bottom ones aren't mine.

 

[gadget73]

no need to even check anything. The 7581A at 35W is more robust than the 6L6GC or 7581, but it's not relevant, because the amplifier does not require a 7581A.

I was specifically meaning the heater current draw there, but wasn't especially clear about it. It was in regards to your mention that the KT66 pulls more heater current than a 6L6 class tube does. I would not be comfortable running a KT66 in place of the stock tubes for that reason.

 

[maxhifi]

I was specifically meaning the heater current draw there, but wasn't especially clear about it. It was in regards to your mention that the KT66 pulls more heater current than a 6L6 class tube does. I would not be comfortable running a KT66 in place of the stock tubes for that reason.

I agree 100%.

 

[Tom Bavis]

I have some GE 7581 that are dual-marked 7581/KT66. But those two are not equivalent - KT66 has higher heater current, higher transconductance. And I wouldn't be surprised to find modern KT66 that are actually relabeled 6L6GC.

 

[Mr Boochie]

They are GE 7581A (not plain 7581). You can use a 7581A in an amp that has original GEC/MOV KT-66 tubes. Will need rebiasing, as usual.

Incidentally, the GEC/MO-V datasheet lists the absolute maximum dissipation for the KT-66 as 30 watts. The designed maximum is 25 watts.

 

[DennisK2021]

You know what is ironic? I've had Harmon-Kardon labeled V-pulls of GE-made (Owensboro, KY) tan-based 7581A tubes.

They are great tubes. And sound great — even biased to the 6L6GC output (30 watts vs. 35 watts max).

Beautiful tubes. They don't make them like this anymore.

I bid on a couple of pairs of those on the bay yesterday. I should have bid more, didn't get them.

Most of the posters here are knowledgeable but are looking at specs. I'm searching on-line sellers for tubes. 6L6GC seems to be tube-store-speak for 5881. As far as I can tell, 7581 non-A does not exist in currently manufactured tubes. They have been replaced by 7581A and the only ones available are Tung Sol. The vintage tubes I've looked at are usually 7581A also.

 

[maxhifi]

I bid on a couple of pairs of those on the bay yesterday. I should have bid more, didn't get them.

Most of the posters here are knowledgeable but are looking at specs. I'm searching on-line sellers for tubes. 6L6GC seems to be tube-store-speak for 5881. As far as I can tell, 7581 non-A does not exist in currently manufactured tubes. They have been replaced by 7581A and the only ones available are Tung Sol. The vintage tubes I've looked at are usually 7581A also.

Have a look at the article on page 4 of this issue of vacuum tube valley. It does a good job explaining the different types of old stock 6L6

https://www.worldradiohistory.com/Archive-All-Audio/Archive-Vacuum-Tube-Valley/Vacuum-Tube-Valley-Issue-04.pdf

 

[Mr Boochie]

Have a look at the article on page 4 of this issue of vacuum tube valley. It does a good job explaining the different types of old stock 6L6

https://www.worldradiohistory.com/Archive-All-Audio/Archive-Vacuum-Tube-Valley/Vacuum-Tube-Valley-Issue-04.pdf

A very good article. Issue 13 has a shootout of various 6L6 types.

 

[Ken Boyd]

What is wrong with some 6L6's, I think they sound great.